A true mainstream Linux distro would need guidelines like this:

• The user is never be expected to type a command into a terminal.
• The user is never be expected to edit a configuration file.
• There is a graphical UI for every possible action the user might want to (or have to) do.

This especially includes:

• Configuring audio devices
• Installing graphics drivers
• Updating the operating system
• Managing applications and storage space
• Connecting to networked storage
• Adjusting kernel parameters (This is neccessary on certain hardware, yet, barely any distro has a graphical UI for it.)

The only distro that comes close to this is Linux Mint, but not even Mint covers everything I just mentioned.

If we want Linux to succeed, there needs to be at least one distro that confidently ships without a terminal.